The Change In Arterial Load During Exercise Is Associated With Differing Arterial And Left Ventricular Patterns

Abstract

Cardiovascular performance is influenced by the interaction between the heart and the arterial system. Arterial elastance (EA) is a measure of the arterial load imposed on the heart that integrates the effects of heart rate (HR), peripheral vascular resistance (PVR) and total arterial compliance (TAC). Normally, HR increases whereas PVR and TAC decrease during exercise. However, there is considerable inter-individual variability in the magnitude of these changes suggesting a wide spectrum of changes in EA during exercise. PURPOSE: To examine whether differing changes in EA during exercise are associated with different patterns of change in arterial and left ventricular properties during exercise. METHODS: 352 subjects (22-93 years; 56% men) without cardiac disease underwent rest and exercise (cycle ergometry) gated blood pool scans to derive EA, PVR, TAC and cardiac volumes. The change in EA during exercise (EAdelta = EApeak - EArest) showed a Gaussian distribution, and the population was stratified according to quartiles of EAdelta. The 1st quartile (Group 1, EAdelta <0.22 mmHg/ml/m2 n=88) was compared to the 4th quartile (Group 4, EAdelta >=0.98 mmHg/ml/m2 n=88). RESULTS: EA groups did not differ in age, sex, systolic BP, or body size. Peak exercise workload was 12% smaller in group 1 vs group 4 (P=0.05). After adjusting for peak workload, EA group 1 had a 54% greater decline in PVR than group 4 (-1459 ± 490 vs -949 ± 515 dyne/sec/cm5/m2, P<0.01), but a similar increase in HR (78 ± 23 vs 86 ± 24 bpm, P=0.42). The most marked difference during exercise was in TAC, which only declined by 13% in group 1 (-0.13 ± 0.5 ml/m2/mmHg), but declined by 58% in group 4 (-0.66 ± 0.3 ml/m2/mmHg). Group 1 also had a 27% greater increase in cardiac index vs group 4 (6.5 ± 1.9 vs 4.8 ± 1.8 l/min/m2, P<0.01), which can be attributed to a greater increase in end-diastolic volume in group 1 vs group 4 (14 ± 11 vs -4 ± 9 ml/m2, P<0.01). CONCLUSION: Our results suggest that individuals with the smallest change in arterial load during exercise have a unique pattern of change in arterial compliance and resistance, and have a greater reliance on the Frank-Starling mechanism to augment cardiac performance during exercise.